1. Field of the Invention
The present invention generally relates to semiconductor devices. More specifically, the present invention relates to a semiconductor device where a semiconductor element and other electronic components are provided on a board, the semiconductor device having a lid thermally connected to the semiconductor element.
2. Description of the Related Art
FIG. 1 is a cross-sectional view of a semiconductor device 1 of an example of a conventional art case. In the semiconductor device 1, a semiconductor element 2 and chip components 4 are mounted on an upper surface of a package board 3. The chip components 4 are, for example, surface terminal type capacitors.
In addition, a lid 5 is provided on the upper surface of the package board 3 so as to cover the semiconductor element 2 and the chip components 4. The lid 5 is thermally connected to the semiconductor element 2 via a thermal connecting member 7. Heat generated from the semiconductor element 2 is radiated by the lid 5 via the thermal connecting member 7. Furthermore, plural solder balls 6 as external connection terminals are provided on a rear surface of the package board 3.
It is general and conventional practice to use resin having insulating properties as the thermal connecting member 7. However, heat generated by such semiconductor elements 2 is increasing due to recent high densification of the semiconductor elements 2. Accordingly, thermal conductivity of the thermal connecting member 7 made of resin is not sufficient and therefore it is not possible to effectively transfer the heat from the semiconductor element 2.
Because of this, instead of the insulating resin, a thermal connecting member made of a metal material having thermal conductivity higher than that of the insulating resin has been used.
However, in a case where solder is used as the metal material forming the thermal connecting member 7, since the solder balls 6 as the external connection terminals are also made of solder, when heat is applied for mounting the semiconductor device 1, the thermal connecting member 7 is made molten along with the solder balls 6. When the thermal connecting member 7 is melted, the thermal connecting member 7 flows along the internal surface of the lid 5 and thereby a part of the thermal connecting member 7 flows down as shown by arrows in FIG. 1 so as to be adhered to the chip components 4. If the thermal connecting member 7 is adhered to the chip components 4 as discussed above, electric shorts are generated in the chip components 4 and therefore the semiconductor device 1 does not properly work.
As a method for not affecting the chip components 4 even if the thermal connecting member 7 is melted and flows down from the lid 5, there is a method (discussed in Patent Document 1 mentioned below) for sealing the chip components 4 with sealing resin 9. FIG. 2A is an expanded view showing a chip component 4 that is sealed by the sealing resin 9.
According to the above-mentioned method, even if the thermal connecting member 7 flows down, since the chip component 4 is protected by the sealing resin 9, it is possible to prevent electric shorts being from being generated in the chip component 4 due to the thermal connecting member 7. [Patent Document 1] Japanese Laid-Open Patent Application Publication No. 60-242647
In the meantime, it is general practice that plural solder arranging parts 8 are provided on a surface of the chip component 4 such as a surface terminal type capacitor. The solder arranging parts 8 are fixed to the package board 3 by the solder. By the soldering, the chip components 4 are mounted on the package board 3. The solder arranging parts 8 as well as the solder balls 6 and the thermal connecting member 7 are made molten when heat is applied for mounting the semiconductor device 1.
However, in a case where the chip components 4 (the solder arranging parts 8) are sealed by the sealing resin 9, flow paths of the molten solder are blocked by the sealing resin 9. In addition, the volume of the solder increases when heat is applied to the solder.
Because of this, the solder melted at the solder arranging parts 8 flows on an interface of the solder arranging parts 8 and the sealing resin 9. At a part where adhesion properties of the solder arranging parts 8 and the sealing resin 9 are low, an electric short is generated neighboring the solder arranging parts 8 as shown by an arrow A in FIG. 2B. Thus, in the case where the sealing resin 9 is provided, while electric shorts due to the molten thermal connecting member 7 can be prevented, the electric shorts may be generated in the sealing resin 9.